Adds three pieces needed to build one KPN network and reuse it across many
replays/configs instead of tearing down and rebuilding per run:
- Channel<T>::push_blocking (+ IVariantChannel/VariantChannel forwarding):
lossless backpressure push that waits for space instead of dropping when
the ring is full. PyNode's run_loop now uses it so a downstream consumer
lagging behind never silently drops a frame.
- PyNetwork::node_ptr / node_stats: raw node handle by name (for a binding
to dynamic_cast to a concrete wrapper and call functor-specific runtime
setters) and a per-node timing snapshot for profiling.
- ObjectVariantNodeWrapper: variant-node adapter for functors that need
runtime-constructed state (a Config, a loaded gallery), mirroring
VariantNodeWrapper's channel plumbing but backed by ObjectNode<Obj>.
Built and used downstream in scene-actor-extraction's sae_kpn Python replay
bindings for repeated threshold-sweep evaluation of the same pipeline.
